1. Field of the Invention
The present invention relates to a method of producing formamide compounds and, more particularly, to a method of producing formamide compounds by formylating amines via transamidation.
2. Description of the Prior Art
Formylated compounds of amines, i.e., formamides are very important materials as solvents, drugs, pesticides as well as intermediates for preparing such solvents, drugs, and pesticides in chemical industries. In order to derive nicotine from nornicotine, it is preferable to produce nicotine via N'-formylnornicotine as an intermediate rather than direct methylation of nornicotine.
Two methods are known for formylating amines. One method involves reaction of an amine with carbon monoxide under heating and high pressure. Another method involves reaction of an amine with separately prepared phenyl formate. However, these methods require relatively complicated reaction procedures and expensive apparatuses.
Another method is also known for producing formamide compounds by formylating amines via transamidation. This method consists of reacting dimethylformamide with an amine under the formylation conditions of the amine. This method has advantages in that dimethylformamide is commercially available at low cost, formylation can be easily performed, and a special apparatus is not needed. In the transamidation reaction, the following equilibrium reaction is established: EQU (CH.sub.3).sub.2 NCHO+R.sup.1 R.sup.2 NH.revreaction.(CH.sub.3).sub.2 NH+R.sup.1 R.sup.2 NCHO
In this reaction, the reactants can be transferred to the products without using a catalyst, by heating to a high temperature to remove the dimethylamine. (Synthesis, 1973, P. 361). This formylation method can indeed produce a desired formamide compound with a high yield, but a long reaction time is required.
In the above literature, an acid catalyst such as sulfuric acid is used in the formylation reaction. When the acid catalyst is used, the reaction time can be shortened to some extent, but other problems such as corrosion of a reaction chamber occur. In addition, since the acid catalyst is a homogeneous catalyst, the reaction product must be washed to remove the acid catalyst after the reaction, and a problem of posttreatments, e.g., a waste fluid disposition, occurs.
As described above, in the conventional method of producing formamide compounds on the basis of the reaction of dimethylformamide and amines, the long reaction time is required if the catalyst is not used. If the acid catalyst is used, the reaction chamber is corroded, and post-treatments are required.